Web service addressing, such as WS-Addressing for a non-limiting example, specifies how to identify address on the Web. When a client starts a service request to a Web service provider, the service provider may assign the client a case number. In the future, the client needs to include that case number for any communication with the service provider and it will be able to look up the case associated with the client. Web service addressing provides a way for the service provider to inform the client about the case number that should be included in every future communications.
Web service addressing can define two interoperable constructs that convey information typically provided by transport protocols and messaging systems. These constructs normalize this underlying information into a uniform format that can be processed independently of transport or application. These two constructs are endpoint (client or service provider) references (EPRs) and message information headers. A Web service endpoint (i.e., service provider) is a referenceable entity, processor, or resource where Web service messages can be targeted. Endpoint references convey the information needed to identify/reference a Web service endpoint, and may be used in several different ways: endpoint references are suitable for conveying the information needed to access a Web service endpoint, but are also used to provide addresses for individual messages sent to and from Web services. To deal with this last usage case, Web service addressing may also define a family of message information headers that allows uniform addressing of messages independent of underlying transport. These message information headers convey end-to-end message characteristics including addresses for source and destination endpoints as well as message identity. Both of these constructs are designed to be extensible and re-usable so that other specifications can build on and leverage endpoint references and message information headers. Some noticeable applications of Web service addressing can include but are limited to: conversation, callback, and asynchronous request response, all discussed in the following context.